The present invention relates to a flowmeter for determining a flow direction of a fluid. The invention also relates to a method for determining a flow direction of a fluid and to an electrical machine having the flowmeter.
In all rating classes of electrical machines, but in particular relatively high-rating machines, a considerable amount of heat is developed which must be dissipated by cooling measures in order to achieve better machine efficiency and/or a longer life. By way of example, air-cooled machines such as generators or motors are known, in particular with ratings of less than 300 MVA, in which cooling is provided by a comparatively large air flow. This air flow may in particular be passed through a line system which comprises numerous flow channels (cf. for example DE 42 42 132 A1 or EP 0 853 370 A1). For example, the flow channels of the line system can be used to force air from the outside inward through the stator of the machine. At the same time, however, air is sucked in by the machine rotor and is forced from the inside outward through the stator, in the opposite direction. If the two airflows are superimposed disadvantageously, the flow ceases to flow within the line system, therefore possibly leading to local overheating of and damage to the machine.
WO 2004/042326 A2 specifies a flowmeter for determining a flow rate of a fluid which is flowing around a measurement element in the flowmeter, such as a gas flow, having an optical waveguide which has a plurality of fiber Bragg gratings and having at least one electrical heating element which is arranged adjacent to the waveguide. This allows the flow rate along the longitudinal extent of the measurement element to be determined from the influence of the temperature on the conductor on an electromagnetic wave which is fed into the optical waveguide. The optical waveguide can be heated via the electrical heating element with a constant amount of heat being applied, resulting in a temperature distribution in the longitudinal direction on the measurement element, corresponding to the local flow rate. This flowmeter is therefore suitable for determining a multiplicity of local flow rates using just one single measurement element. However, it is not possible to determine the direction into which the fluid is flowing relative to the measurement element.